An investigation of the occurrence and nature of the transport and metabolism of purines and their derivatives in Crithidia. This will involve the use of labeled (radioactive) compounds and an identification and quantitation of all metabolic products, by the use of gel and paper electrophoresis, column and paper chromatography and electrofocusing. BIBLIOGRAPHIC REFERENCES: Kidder, G.W. and Nolan, L.L., Enzymatic synthesis of labeled carbamylaspartic acid., Biochem Biophys. Res. Comm., 65, 420, (1975). Kidder, G.W., Dewey, V.C. and Nolan, L.L., Enzymes of the orotate biosynthetic pathway in Crithidia fasciculata. Can. J. Biochem., 54, 32 (1976).